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Re: [TCML] Homemade Crookes Tube?



Paul, David is absolutely correct. I test semiconductors for radiation hardness using x-rays and the tube you had made sounds like it has low pressure argon gas and there is also a small amount of mercury on one of the electrodes when a " neon" tube is made. I say neon but tube color depends on which gas is in the tube and the phosphorous coating inside of the tube. I can assume your tube is plain glass with no coating. I had one of every color made years ago by our local neon sign company and I hold one end in my bare hand and arc to my tesla coils at the other end. You need to wrap each end with aluminum foil to spread the power out when holding it. Dangerous x-rays require a minimum voltage of 30 kV with some tubes operating with as much as 200 kV. Tungsten is the typical target and a very hot high current filament is necessary to produce powerful 10 keV and higher x-rays. The super hot filament is required to emit enough electrons to generate the x-rays. What you have is not much different than using a fluorescent lamp to arc to the secondary output.

A Bishop
Principal Device Physics Tech

Sent from my iPad

> On Sep 18, 2014, at 7:05 PM, David Rieben <drieben@xxxxxxx> wrote:
> 
> Paul,
> 
> I am certainly no authority on this matter but from what I have gleaned, you are not going to produce "hard" x-rays in this manner. Besides the hard vacuum, this would also require a white-hot filament (for an electron source) for the cathode, a heavy metal target (usually tungsten) for the anode, and well over ~50  kVDC potential between the said cathode and anode to really produce the ionizing, body penetrating hard x-rays (even dental x-ray tubes typically run about 70 kV(DC)). That being said, if you are powering your tube with say 10 to 20 kVDC, you may produce some low energy "soft" x-rays, but I don't think it's going to be a significantly ionizing radiation source. I'm not even sure if you can produce any kind of x-rays at all with AC? That's just "my" 2 cents. ;^)
> 
> David
> 
> 
> On Thursday, September 18, 2014 6:01 PM, Paul B. Thompson <mrapol@xxxxxxxxxxxx> wrote:
> 
> 
> 
> I just recently found a local neon sign maker and asked him to make me a 
> simple vacuum tube, which he did, gratis (!). It's 18 inches long, clear 
> glass tubing about 3/4 inch in diameter, with electrodes at opposite ends. I 
> don't know how hard a vacuum he pulled on this, but very quick tests show a 
> pale blue glow from end to end. A strong magnet placed next to the tube 
> pinches the beam, intensifying it at the spot.
> 
> I've not run this for more than a few seconds. I am concerned about x-rays. 
> I'd like advice about operating this tube safely.
> 
> Thanks,
> 
> Paul 
> 
> 
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